Abstract
We investigate the Cauchy problem for the nonlinear damped wave equation u(tt) - Delta u + u(t) = vertical bar u vertical bar(p) + vertical bar del u vertical bar(q) + w(x), where N >= 1, p, q > 1, w is an element of L-loc(1) (R-N), w >= 0 and w not equivalent to 0. Namely, we first obtain the Fujita critical exponent for the considered problem. Next, we determine its second critical exponent in the sense of Lee and Ni. In particular, we show that the nonlinear gradient term vertical bar del u vertical bar(q) induces a phenomenon of discontinuity of the Fujita critical exponent.